Magnetic beam positioning device



United States Patent O 3,192,452 MAGNETIC BEAM POSITIONING DEVICE John L. Rennick, Elmwood Park, lll., assignor to Zenith Radio Corporation, Chicago, lll., a corporation of Delaware Filed Mar. 4, 1963, Ser. No. 262,744 7 Claims. (Cl. 317-200) The present invention relates to color television and, more particularly, to beam positioning devices for use with multi-beam color kinescopes.

In color television receivers and other systems using multi-beam cathode-ray tubes, proper operation requires that several beams be converged to a common point on the luminescent screen. Both static and dynamic convergence adjustments are normally required to direct the beams along desired paths of transit. Static convergence is customarily accomplished through the use of permanent magnets which, in conjunction with suitable internal pole pieces in the color kinescope, are so adjusted that the resulting static magnetic fields can converge the electron beams, in the absence of scanning fields, at the center of the luminescent screen. Dynamic convergence fields are conventionally established by electromagnets which also cooperate with the internal pole pieces and are responsive to convergence signals which vary as a function of scanning deflection. Most of the required magnets are usually assembled upon a common convergence yoke mounted on the neck of the color kinescope.

The conventional static convergence adjustments of a convergence yoke provide radial movement of the three beams and, because of the geometric configuration of the gun cluster, an additional magnet is normally required to provide lateral movement of one of the beams as conventional radial adjustment will move only two of the three beams both vertically and laterally. There is no adjustment for laterally moving the third beam in the conventional convergence yoke. The additional magnet employed, customarily referred to as the blue beam lateral magnet, cooperates with suitable internal pole pieces within the neck of the tube and, in one arrangement, provides independent lateral movement of the third or blue beam. In another arrangement wherein the additional magnet is repositioned on the tube neck, lateral movement of the blue beam relative to the lateral movement of the remaining two beams is provided. With this arrangement all three of the beams are affected by the magnetic iield of the blue beam lateral magnet.

Although there have been numerous blue beam lateral magnet devices employed in the past, all produced a certain amount of stray magnetic fields which tend to affect the paths of the beams and make the convergence adjustments more difficult. There have been numerous devices employed to reduce these stray fields but they have not been found to be completely satisfactory.

The principal object of this invention is to provide a new and improved beam positioning device for use with a multi-beam cathode-ray tube.

Another object of this invention is to provide a blue beam lateral magnet device for use with a multi-beam color cathode-ray tube.

It is also an object of this invention to provide a blue beam lateral magnet device which has a minimal amount of stray field effects and is of greatly simplied construction.

The invention contemplates a magnetic device for use with a cathode-ray tube in which multiple electron beams may have departures from desired paths of transit to the screen. This magnetic device comprises a unitary elongated structure having at least two spaced magnets oriented such that the ends of the structure are of opporice site magnetic polarity. The device includes means for maintaining the unitary structure on and oriented radially of the neck of the cathode-ray tube. Also, the umtary structure is adjustably retained with either of the poles of the unitary structure in proximity to the path of one of the beams whereby the position of the poles with respect to the path of the one electron beam may be varied to reduce the magnitude of departure of the one beam from its desired path of transit.

The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood, however, by reference to the following description taken in conjunction with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE 1 is a cross-sectional view, partly broken away, of a preferred embodiment of the invention in its position about the neck of a multi-beam cathode-ray tube;

FIGURE 2 is a fragmentary cross-sectional view taken along lines 2-2 of FIGURE 1 and;

FIGURE 3 is a perspective view, partly in section, of the embodiment shown in FIGURE 1.

Referring to FIGURES 1 and 3, a preferred embodiment of the invention is shown mounted on the neck 9 of a multi-beam cathode-ray tube such as a conventional tri-beam color kinescope having a conventional base socket 8. In cathode-ray tubes of this type, the cylindrical axis of the neck of the tube is generally coincident with the geometric axis of symmetry of the entire tube. Within the neck portion of the cathode-ray tube are internal pole pieces 11, 12. Pole piece 11 is a partially closed upright channel while pole piece 12 is of a generally U-shaped configuration having upright legs follow- -ing the curvature of the tube neck. Electron beams 13, 13, and 13" are emitted from respective electron guns (not shown) and are directed in such a manner so that beam 13 passes through a grid electrode 10 positioned between pole piece 11 and the inner bight surface of pole piece 12 while beams 13 and 13 pass respectively through grid electrodes 10' and 10 positioned along the outer bight surface of pole piece 12. Beam 13 is associated with the blue color producing phosphor while beams 13, 13 are respectively associated with the red and green color producing phosphors.

The embodiment shown in FIGURES 1 and 2 comprises a molded unitary spring or collar 17 constructed of resilient material and having a normal inner dimension slightly less than the neck radius of the cathode-ray tube. Spring 17 is hexagonal in form with one of the sides having a radial opening or window 18 therein for accepting a collar element 19. Collar 19 has an inner end surface 20 of a curvature approximating the curvature of the neck of the tube while the opposite end portion of collar 19 which projects through opening 18 is of reduced cross-sectional area. Additionally, collar element 19 has a counterbore 25 for accepting an outstanding elongated resilient split sleeve 26.

A rod 30 comprising ferromagnetic material is slidably retained in sleeve 26 so as to be oriented radially of the tube neck, while a metallic flux-shorting ring 31 circumscribes the sleeve and resiliently retains rod 30 in sleeve 26. Rod 30 is a unitary elongated structure, having at least two spaced magnets oriented such that the ends of the structure are of opposite magnetic polarity. One end of rod 30 is of a north polarity while the opposite end of the rod is of a south polarity. The other pole of each magnet is spaced inwardly a short distance from the respective adjacent rod end.

In Aassembling this embodiment of the invention, the

initial step is performed by inserting the collar 19, which serves as means for maintaining the unitary structure 30 on the neck of the cathode-ray tube, into window 18 of spring 17. Sleeve 26 is inserted into counterbore 25 of collar 19 and flux shorting ring 31 is slipped into place at the end of the sleeve away from collar element 19. If desired, sleeve 26 and collar 19 may comprise a unitary molded structure; in a further modification, the latter two elements are unitary with spring 17. Rod 30 is inserted into sleeve 26 and retained therein by the resilient force of sleeve 26 and flux shield 31. Rod 30 is thus slidably retained so that the position of the poles of the magnet with respect to the path of at least one of the electron beams may be varied. Being coupled to collar 19, sleeve 26 also serves in this instance as means for adjustably retaining either of the poles of the unitary magnet structure in proximity to the path of the electron beams.

After the magnetic device is assembled, it may be easily slid onto the picture tube neck. The side portions of hexagonal spring 17 provide sufficient resilience to allow the device to be slid over the tube base and to readily adapt to cathode-ray tube necks of slightly varying diameters within the range of manufacturing tolerances. The device is moveable both rotationally and longitudinally so that one end of rod 30 may be positioned over one leg portion of U-shaped pole 12.

As previously mentioned, the electron beams pass adjacent the respective pairs of internal pole pieces. Magnetic fields between these pole pieces, being generally perpendicular to the direction of electron motion, cause a resulting lateral deflection of the beams which is proportional in amount to the strength of the impressed magnetic field. By suitably adjusting the impressed magnetic field strength, the beams can be directed to converge at a given point or points on the luminescent screen. For purposes of explanation, beams 13, 13 and 13" will be respectively referred to as the blue, red and green beams.

As shown in FIGURE 1, fiux coming from the north pole of magnetic rod 30 reaches one leg of pole piece 12 and, after passing through a portion of the pole piece, divides into two fiux paths. On one path, the flux passes through the path of travel of the blue beam, to pole piece 11 and then back to the south pole adjacent to the north pole nearest the tube neck. On the other path, the flux passes through the paths of travel of the red and green beams and then back to the adjacent south pole.

After conventional radial static convergence adjustments of the type previously explained are made, the three electron beams, when viewed at the screen, appear to be in a horizontal line. The red and green beams are superposed while the blue beam is spaced apart from the two superposed beams. As the finx density in the tube neck is varied by changing the position of rod 30 with respect to the pole piece 12, the blue beam moves toward the grouped beams while the grouped beams move toward the blue beam. Although there is lateral movement of the grouped beams, the blue beam moves further for a given change in the field intensity. Consequently, the blue beam will become superposed with the red and green beams, providing complete static convergence of the three beams. The blue beam travels further than the grouped red and green beams with a change in the magnitude of the flux field due to the greater ux density in the region of the blue beam path occasioned by pole piece 11.

Asis well known, the direction of lateral motion of the beams is determined by the polarity of the magnetic field through which the beams pass. To bring about this change in direction, rod 30 may be removed and inserted so that the south pole is now nearest pole piece 12, thereby producing a field in the tube neck in the opposite direction. In some instances it may be desirable not to have any flux from rod 30 passing through the pole pieces. To this end, ring 31 is of a low reluctance ma- 4 terial. As shown in FIGURE 3, when magnetic rod 30 is Withdrawn from sleeve 26 to a position where its end closest to the tube neck is adjacent ring 31, substantially no flux passes through the pole pieces 11, 12, as the pair of magnetic poles nearest the tube are rendered ineffective.

As a feature of the invention, rod 30 contains two pairs of magnetic poles as previously explained. This arrangement is desirable because the reduction of stray magnetic fields is of prime importance in obtaining complete, accurate convergence of the beams. When the stray flux paths to and from the poles of the magnet are made as short as possible, the stray magnetic fields are minimized. As shown in FIGURE 1, a north and south pole pair is located in one end portion of rod 30 and the fiux emanating from the north pole closest the tube neck returns to the adjacent south pole rather than to the remote end of the rod 30 as would be conventional practice. Similarly, when the magnet is inserted so that the south pole is nearest pole 12, the flux return path is to the next adjacent north pole rather than to the opposite end of rod 30.

While the magnetic structure 30 of FIGURE 1 is shown as a single ferromagnetic rod permanently magnetized with the appropriate poles, a cylindrical tube having two individual permanent magnets each having north and south poles may be employed.

The elongated construction of rod 30 is also advantageous because it permits the closely spaced active pole pair to be firmly retained adjacent the tube neck by an extended clamping surface. At the same time, the inactive pole pair end of rod 30 is readily accessible to permit adjustment of the activeV pole pair.

Thus, the invention takes the form of a new and improved beam positioning device for use with a multi-beam cathode-ray tube. The embodied blue beam lateral device achieves -a reduction of stray magnetic fields and is of simplified construction. Furthermore, maximum simplicity of adjustment is provided.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made therein without departing from the invention in its broader aspects. The aim of the appended claims, therefore, is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. A magnetic device for use with a multiple-beam cathode-ray tube in which electron beams may have departures from desired paths of transit to the screen, said device comprising:

a unitary elongated structure having two spaced magnets oriented such that the ends of said structure are of opposite magnetic polarity;

and means for maintaining said unitary structure on and oriented radially to the neck of said cathode-ray tube and adjustably retaining said poles of said unitary structure selectively in proximity to the path of one electron beam, whereby the position of said poles with respect to the path of said electron beam may be varied to reduce the magnitude of departure j of said beam from its desired path of transit.

2. A magnetic device for use with a multiple-beam cathode-ray tube in which electron beams may have departures from desired paths of transit to the screen, said device comprising:

a unitary elongated structure having two spaced magnets oriented such that the ends of said structure are of opposite magnetic polarity;

means for maintaining said unitary structure on the neck of said cathode-ray tube;

and means coupled to said maintaining means, for adjustably retaining either of said poles of said unitary structure selectively in proximity to the path of one electron beam whereby the position of said poles with respect to the path of said electron beam may be varied to reduce the magnitude of departure of said one beam from its desired path of transit. 3. A magnetic device for use with a multi-beam cathode-ray tube in which the electron beams may have departures from desired paths of transit to the screen, said device comprising: a unitary elongated structure having two spaced magnets oriented such that the ends of said structure are of opposite magnetic polarity;

means for maintaining said unitary structure on and oriented radially to the neck of said cathode-ray tube and adjustably retaining said poles of said unitary structure selectively in proximity to the path of one electron beam, whereby the position of said poles with respect to the path of said electron beam may be varied to reduce the magnitude of departure of said one beam from its desired path of transit;

and magnetic ux shorting means, coupled to said retaining means, for selectively rendering at least one pair of poles of said unitary structure ineffective.

4. A magnetic device for use with a multi-beam cathode-ray tube in which the electron beams may have departures from desired paths of transit to the screen, said device comprising: a unitary elongated structure having two spaced magnets oriented such that the ends of said structure are of opposite magnetic polarity;

-means for maintaining said unitary structure on and `oriented radially to the neck of said cathode-ray tube and adjustably retaining said poles of said unitary structure selectively in proximity to the path of one electron beam, whereby the position of said poles with respect to the path of said electron beam may be varied to reduce the magnitude of departure of said one beam from its desired path of transit;

and magnetic flux shorting means, coupled to said retaining means, for selectively rendering the one of said pole pairs nearest said neck inefective.

5. A magnetic device for use with a multiple-beam cathode-ray tube in which electron beams may have departures from desired paths of transit to the screen, said device comprising:

a unitary elongated structure having two spaced magnets oriented such that the ends of said structure are of opposite magnetic polarity;

and means for maintain-ing said unitary structure -on and oriented radially to the neck of said cathode-ray tube and for adjustably retaining said poles of said unitary structure selectively in proximity to said beam paths whereby the position of said poles with respect to said beam paths may be varied to alter the paths of transit of said beams.

6. A magnetic device for use with a tri-color cathoderay tube in which red, blue, and green phosphor exciting electron beams may have departures from desired paths of transit to the screen, said device comprising:

a unitary elongated structure having two spaced magnets oriented such that the ends of said structure are of opposite magnetic polarity;

means for maintaining said unitary structure on and oriented radially of the neck of said cathode-ray tube and enabling movement of one of said poles of said unitary structure selectively toward and away from the paths of said electron beams to deflect said blue phosphor exciting beam in one direction toward its desired path of transit and said red and green phosphor exciting beams in an opposite direction toward their desired paths of transit.

7. A magnetic device for use with a tri-color cathoderay tube in which red, blue, and green phosphor exciting electron beams may have departures from desired paths of transit to the screen, said device comprising:

a single ferromagnetic rod having at least two spaced pairs yof magnetic poles oriented `such that the ends of said r-od are of opposite magnetic polarity;

spring means on the neck of said cathode-ray tube;

sleeve means, coupled to said spring means for accepting and adjustably retaining said rod oriented radially of the tube neck and in a position to deflect said blue phosphor exciting beam in one direction toward its desired path of transit and said red and green phosphor exciting beams in an opposite direction toward their desired paths of transit; and magnetic ux-shorting means, coupled to said sleeve means, for selectively rendering at least one pair of poles of said rod ineffective.

References Cited by the Examiner UNITED STATES PATENTS 2,769,110 10/56 Obert 317-200 2,806,164 9/57 Clay et al. 317-200 2,854,607 9/58 Niklas et al. 317-200 JOHN F. BURNS, Primary Examiner. 

1. A MAGNETIC DEVICE FOR USE WITH A MULTIPLE-BEAM CATHODE-RAY TUBE IN WHICH ELECTRON BEAMS MAY HAVE DEPARTURES FROM DESIRED PATHS OF TRANSIT TO THE SCREEN, SAID DEVICE COMPRISING: A UNITARY ELONGATED STRUCTURE HAVING TWO SPACED MAGNETS ORIENTED SUCH THAT THE ENDS OF SAID STRUCTURE ARE OF OPPOSITE MAGNETIC POLARITY; AND MEANS FOR MAINTAINING SAID UNITARY STRUCTURE ON 